Method for monitoring and controlling a chemical process

• US 5,262,961 A
• Filed: 12/17/1990
• Issued: 11/16/1993
• Est. Priority Date: 12/17/1990
• Status: Expired due to Term

• Current Assignee: Applied Power Concepts Incorporated
• Original Assignee: Applied Power Concepts Incorporated
• Inventors: Farone, William A.
• Primary Examiner(s): Teska, Kevin J.
• Application Number:
  US07/628,321
• Time in Patent Office: 1,065 Days
• Field of Search: 364/496, 364/497, 364/498, 364/499, 364/550, 364/554
• US Class Current: 702/23
• CPC Class Codes: G01J 3/28 Investigating the spectrum using colour filters G01J3/51
• CPC Class Codes: G01N 2021/3595 using FTIR
• CPC Class Codes: G01N 2021/8411 Application to online plant, process monitoring
• CPC Class Codes: G01N 21/27 using photo-electric detection G01N21/31 takes precedence; circuits for computing concentration logarithmic circuits G06G7/24; photometric circuits in general G01J
• CPC Class Codes: G01N 2201/129 Using chemometrical methods

Abstract

An on-line method of monitoring and controlling a chemical process is based on measuring the concentration of process reactants and products using spectrometric technology. The spectral data is analyzed using a modified chi-squared processing method to determine the unknown concentration of reactants and products in test samples withdrawn from the process. This method avoids the need for the spectral data to conform to Beer'"'"'s Law and the best spectral range is determined automatically. The physical parameters of the process are monitored and altered based on this determination as required to optimize the process.

Claims

1. Using a general purpose computer having memory and an electromagnetic spectrum analysis instrument, a method of determining the concentrations of a plurality of different ingredients present over a concentration range in a chemical process, comprising

(I) first creating data files in the computer memory by

(a) preparing a number of calibration samples at different concentrations spanning said concentration range for each individual ingredient being monitored,

(b) measuring the electromagnetic absorption of the calibration samples at a selected number of different wavelengths over a predetermined range of wavelengths of the electromagnetic spectrum and storing the measurements in a first data file in the memory of the computer,

(c) repeating steps (a) and (b) a sufficient number of times to obtain statistically significant data composed of these absorbance measurements for the known concentrations of each of the ingredients and storing said data in a second data file in the memory of the computer,

(d) using the computer, the data in said first and second data files, and the following equations ##EQU4## where A is the absorbance measurement of each individual calibration sample, and

c is the concentration in molar units of the ingredient in the calibration sample,

k_solvent (for liquids and solids) is the absorbance value of the component designated as a solvent in which the other components are distributed measured in its pure form,

calculating for each calibration sample an average k value at each of said selected number of different wavelengths over said predetermined range of wavelengths, and a standard deviation value thereof, and storing said calculated k values and standard deviation values thereof in a third data file in the memory of the computer,

(e) preparing a plurality of calibration sample mixtures of the ingredients at known concentrations and measuring the electromagnetic absorption of the calibration sample mixtures at each wavelength within said range of wavelengths of the electromagnetic spectrum,

(f) using the computer and the data in said third data file determining which wavelength within said range of wavelengths of the electromagnetic spectrum shall provide a solution to the following equations to an acceptable level of precision by solving said following equations to determine the respective concentrations of the ingredients in the calibration sample mixtures using (i) an arbitrarily selected number of wavelengths within said range of wavelengths, (ii) the lowest standard deviation among the average k values as determined in step (d), and (iii) the singular value decomposition mathematical technique to determine which of the arbitrarily selected number of wavelengths provide the lowest chi-squared statistic between calculated and known values of the concentration of ingredients in the calibration sample mixtures

2. Based on real time measurements, an on-line method of controlling a chemical process producing an effluent stream in which a plurality of ingredients are present at different concentrations over a concentration range depending on predetermined variable conditions occurring in the process,

said method comprising

monitoring the concentrations of the ingredients present in said effluent stream, and

altering said process conditions as determined by absorption data of the effluent stream taken with an electromagnetic absorption instrument and using a general purpose computer having memory to adjust control device that regulate said process conditions to produce a desired concentration of ingredients in the effluent stream,

said absorption data reflecting essentially accurately the concentration of the ingredients in the effluent stream as determined by a method, comprising

(I) first creating data files in the computer memory by

(a) preparing a number of calibration samples at different concentrations spanning said concentration range for each individual ingredient being monitored,

(b) measuring the electromagnetic absorption of the calibration samples at a selected number of different wavelengths over a predetermined range of wavelengths of the electromagnetic spectrum and storing the measurements in a first data file in the memory of the computer,

(c) repeating steps (a) and (b) a sufficient number of times to obtain statistically significant data composed of these absorbance measurements for the known concentrations of each of the ingredients and storing said data in a second data file in the memory of the computer,

(d) using the computer, the data in said first and second data files, and the following equations ##EQU5## where A is the absorbance measurement of each individual calibration sample, and

c is the concentration in molar units of the ingredient in the calibration sample,

k_solvent (for liquids and solids) is the absorbance value of the component designated as a solvent in which the other components are distributed measured in its pure form,

calculating for each calibration sample an average k value at each of said selected number of different wavelengths over said predetermined range of wavelengths, and a standard deviation value thereof, and storing said calculated k values and standard deviation values thereof in a third data file in the memory of the computer,

(e) preparing a plurality of calibration sample mixtures of the ingredients at known concentrations and measuring the electromagnetic absorption of the calibration sample mixtures at each wavelength within said range of wavelengths of the electromagnetic spectrum,

(f) using the computer and the data in said third data file determining which wavelength within said range of wavelengths of the electromagnetic spectrum shall provide a solution to the following equations to an acceptable level of precision by solving said following equations to determine the respective concentrations of the ingredients in the calibration sample mixtures using (i) an arbitrarily selected number of wavelengths within said range of wavelengths, (ii) the lowest standard deviation among the average k values as determined in step (d), and (iii) the singular value decomposition mathematical techniques to determine which of the arbitrarily selected number of wavelengths provide the lowest chi-square statistic between calculated and known values of the concentration of ingredients in the calibration sample mixtures

3. An on-line method of monitoring and controlling a chemical process having physical parameters and where the concentration of process components is measured, comprising

(a) measuring the concentration of process components in samples from the process using a spectrometric instrument to obtain spectral data characteristic of the process components,

(b) analyzing the spectral data using a chi-squared mathematical technique to determine the unknown concentration of process components in said samples, and

(c) monitoring the physical parameters of the process and altering said physical parameters based on the determination of concentration of process components in step (b) as required to optimize the process.